The present invention relates to a flow controller, which has a first port and a second port and which is capable of flowing a fluid from the second port to the first port as controlled flow, whose flow volume is controlled, and flowing the fluid from the first port to the second port as free flow.
A conventional flow controller is disclosed in Japanese Patent Kokai Gazette No. 6-331059, and the conventional flow controller is shown in FIG. 15.
A main body 80 of the flow controller has an opening section 82, which acts as a first port, and an opening section 84, which acts as a second port. A control member 88 having a control hole 86, through which a fluid passes, is provided in a flow path, which makes the first port 82 and the second port 84 communicate each other. A needle 90 is capable of moving in the axial direction and entering the control hole 86. By varying a length of inserting a tapered end of the needle 90 into the control hole 86, a sectional area of a clearance formed in the flow path, through which the fluid can pass, is varied, so that flow volume of controlled flow can be controlled (see paragraph 0015 of the Japanese patent kokai gazette No. 6-331059). The axial movement of the needle 90 is adjusted by manually rotating a rotary member 92.
An outer flow path, which makes the first port 82 and the second port 84 communicate each other, is formed outside of the control member 88. A diaphragm 94, which acts as a check valve, is provided in the outer flow path. The diaphragm 94 prohibits the fluid to flow from the second port 84 to the first port 82 via the outer flow path; the diaphragm 94 allows the fluid to flow from the first port 82 to the second port 84 via the outer flow path (see paragraphs 0013 and 0015-0017 of the Japanese patent kokai gazette No. 6-331059).
As described above, in the conventional flow controller shown in FIG. 15, the flow volume of the controlled flow is controlled by adjusting the sectional area of the clearance between an outer face of the needle 90 and an inner face of the control hole 86. The sectional area can be adjusted by moving the needle 90 with respect to the control hole 86.
However, it is difficult to precisely control the flow volume of the controlled flow when the flow volume is small. This disadvantage will be explained with reference to FIGS. 16A and 16B.
In FIG. 16A, no clearance is formed between the outer face of the needle 90 and the inner face of the control hole 86. Namely, no controlled flow passes. In this state, the needle 90 is moved so as to form the clearance C between the outer face of the needle 90 and the inner face of the control hole 86. The state of forming the clearance C is shown in FIG. 16B. The clearance C is formed around an entire circumference of the needle 90.
To flow the controlled flow with small flow volume, the needle 90 in the state shown in FIG. 16A is slightly moved. However, the clearance C is formed around the entire circumference of the needle 90, so the sectional area of the clearance C rapidly increases. Therefore, it is difficult to precisely control the flow volume of the controlled flow when the flow volume thereof is small.
Further, fluid resistance strongly works to the tapered needle 90, so the needle 90 must be made of a high rigidity material, e.g., steel, so as to secure enough strength of the needle 90. Therefore, it is difficult to reduce weight and a production cost of the flow controller.